The Hydrosphere

What Is This Module About?

Water, also known as the “universal solvent,” has several properties. It undergoes several
processes. Human beings as well as plants and animals cannot live without fresh, clean water.
Where does water come from? How is water used to produce geothermal energy? What is
geothermal energy used for? These and other questions will be answered as you study this
module.
This module is made up of two lessons:
Lesson 1 – Water Around Us
Lesson 2 – What Is Water For?

What Will You Learn From This Module?

After studying this module, you should be able to:

♦ identify the different phases of water;
♦ explain the water cycle;
♦ enumerate the uses of water;
♦ identify the effects of salt intrusion and pollution on the different bodies of water; and
♦ identify possible solutions to these problems.

1
 Let’s See What You Already Know

Before studying this module, take this simple test first to find out how much you already
know about the topics in this module.
Write True if the statement is correct and False if it is wrong.
_____ 1. The phases of water include: solid, liquid, gas and plasma.
_____ 2. The pictures below show in the correct order the solid, liquid and gaseous
phases of water.

_____ 3. About 3% of the earth’s surface water is freshwater while 97% is salt water.
_____ 4. The four great oceans are the Pacific, the Atlantic, the Indian and the Antarctic
oceans.
_____ 5. Evaporation is the process of turning water into vapor.
_____ 6. The surface area of the world’s total waters is five times bigger than that of
land.
_____ 7. The process wherein water from the earth’s surface circulate to the
atmosphere and back is called the water cycle.
_____ 8. Condensation is the process of returning water vapor to its original liquid state.
_____ 9. Our country has geothermal stations in Albay, Laguna, Leyte and Negros
Oriental.
_____ 10. Geothermal energy can only be utilized if there is an underground supply of
superheated steam.
Well, how was it? Do you think you fared well? Compare your answers with those in the
Answer Key on page 19 to find out.
If all your answers are correct, very good! This shows that you already know much about
the topics in this module. You may still study the module to review what you already know. Who
knows, you might learn a few more new things as well.
If you got a low score, don’t feel bad. This only means that this module is for you. It will
help you understand some important concepts in your daily life. If you study this module carefully,
you will learn the answers to all the test items and a lot more. Are you ready?
You may go now to the next page to begin Lesson 1.

2
 LESSON 1

Water Around Us

Did you know that the earth is sometimes called the “blue planet”? This is because of
the water that covers 71% of the earth. Even if the oceans compose the greater part of the
earth’s surface, it was only recently that they became an important focus of study.

After studying this lesson, you should be able to:

♦ identify the phases of water and differentiate them from each other; and
♦ explain the water cycle.

Let’s Study and Analyze

Study the diagram below. Then answer the questions on the next page.

Precipitation

Water evaporates
from the lake

Water vapor
released into the
atmosphere
by trees and
other plants
Water vapor
evaporates
from the sea

River flows Water seeps

into the sea underground
and flows to the sea

The water cycle

3
 1. Where does more water evaporate from—land or bodies of water?
_________________________________________________________________
2. How do you know that water condensed in the air?
_________________________________________________________________
3. What are some of the ways by which water from land go back to the oceans?
_________________________________________________________________
4. What phase changes take place as snow melt and finally evaporate?
_________________________________________________________________
Compare your answers with those in the Answer Key on page 19. How well did you do?

Let’s Learn

Water is a compound consisting of two atoms of hydrogen and one atom of oxygen. It is a
colorless, odorless and tasteless liquid. It has a freezing point of 0°C and a boiling point of
100° C at one atmospheric pressure.
Water can exist in four phases—solid, liquid, gas and plasma. But for the purposes of our
discussion, we will only focus on the first three phases.
Water when solid is called ice. In addition to oceans, lakes and rivers, significant amounts of
water are locked into the earth’s polar ice caps and glaciers, which are bodies of ice that form in
regions where snowfall exceeds melting. Ice caps are layers of ice that form at the north and
south polar regions of the earth. Avalanches are large bodies of ice that slowly fall down a slope
or valley under the influence of gravity. Approximately 96% of glaciers occur in Antarctica and
Greenland, while the rest are widely scattered in mountainous areas throughout the world. All of
these places where water occurs tap into the same central supply. During its lifetime, a given
molecule of water will cycle through many different kinds of bodies over and over again.

When water is in its gaseous state, it is called vapor. This is also odorless, colorless and
tasteless and mixes freely with the other gases in the atmosphere. It can change from one phase to
another with relative ease at certain temperatures and pressures. This ability allows water to leave
oceans as gas and return again as liquid.

4
 The water cycle involves the short-term, back-and-forth transfer of water molecules
between the oceans and the land. Water evaporates off the surface of the ocean, forms into
clouds, falls as rain on the land and then returns to the oceans via rivers and streams. Most
terrestrial life depends upon this simple cycle.

Condensation

Precipitation
Evaporation from oceans
Evaporation from plants

Runoff — to lakes, rivers, oceans Evaporation from lakes, rivers

Runoff — to ocean

Groundwater

To lakes, rivers

To plants

To oceans

To ground storage

A big part of this cycle remains unseen, however. Some of the water that falls on the
continents does not immediately return to the oceans, rather, it seeps into the earth to become
groundwater. Groundwater may move into large aquifers, which are bodies that act as
underground storage tanks of water. By some estimates, more than 98% of the world’s
freshwater is stored as groundwater.

Let’s Review

Narrate the water cycle in your own words. Use the space provided below for your answer.
__________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Compare what you wrote with the sample answer in the Answer Key on page 19. How
well did you do?

5
 Let’s Learn

Different processes can alter water from one phase to another. Let us take a look at some
of them below.
Evaporation
Evaporation of water from the earth’s surface forms one part of the water cycle. At
100°C, the boiling point, all water will rapidly be turned to vapor, for the energy supplied to the
water is enough to break apart all the molecular bonds in it. At temperatures between 100°C and
0°C, only some of the molecules in the water have enough energy to escape to the atmosphere
and the rate at which water is converted to vapor is much slower.

The rate of evaporation will depend upon a number of factors. The rate of evaporation
increases when temperature increases. An increase of 10°C will approximately double the rate of
evaporation. The humidity of the surrounding air will also influence evaporation. Drier air has a
greater “thirst” for water vapor than humid, moist air. It follows, therefore, that the presence of
wind will also increase the rate of evaporation. On still days, water evaporating to the air remains
close to its source, increasing the local humidity. As the moisture content of the air increases, the
rate of evaporation diminishes. If, however, a steady flow of air exists to remove the newly-
formed vapor, the air surrounding the water source will remain dry, “thirsty” for future water.

Let’s Try This

To see how evaporation takes place, do the following activity.

Get two dishes. Put about 10 ml (2 tsps.) of water in each dish. Place one dish under the
sun or if the sun isn’t shining, place it under and close to a light source. Place the other dish in the
shade. Observe each dish every four hours overnight and record what happens to the water each
time.
Is the process of evaporation clear to you now?

6
 Let’s Learn

Let us now study another process in the water cycle.

Transpiration
Transpiration is the evaporation of water from plants. It occurs chiefly at the leaves while
their stomata are open for the passage of carbon dioxide and oxygen during photosynthesis.

There are several environmental factors that affect the rate of transpiration and these are:
1. Light
Plants transpire more rapidly when there is light. This is largely because light
stimulates the opening of the stomata. Light also speeds up transpiration by warming
the leaves.
2. Temperature
Plants transpire more rapidly at higher temperatures because water evaporates
more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast
as it does at 20°C.
3. Humidity
The rate of diffusion of any substance increases as the difference in concentration
of the substances in the two regions increases. When the surrounding air is dry,
diffusion of water out of the leaf occurs more rapidly.
4. Wind
When there is no breeze, the air surrounding a leaf becomes increasingly humid
thus reducing the rate of transpiration. When a breeze is present, humid air is carried
away and replaced by drier air.

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 5. Soil Water
A plant cannot continue to transpire rapidly if its water loss is not replaced from
the soil. When absorption of water by the roots fails to keep up with the rate of
transpiration, loss of turgor occurs and the stomata close. This immediately reduces the
rate of transpiration. If the loss of turgor extends to the rest of the leaf and stem, the
plant wilts.
Condensation
Condensation is the process whereby water vapor in the atmosphere is returned to its
original liquid state. In the atmosphere, condensation may appear as clouds, fog, mist, dew or
frost, depending upon the physical conditions of the atmosphere. Condensation is not a matter of
one particular temperature but of a difference between two. Condensation of water vapor occurs
when the temperature of air is lowered to its dew point.

All air contains water vapor of varying quantities. The lower the air temperature, the smaller
the maximum possible capacity for vapor. When air is cooled, relative humidity increases, until at
a particular temperature called the dew point, the air becomes saturated. Further cooling below
the dew point will induce condensation of the excess water vapor.
The temperature of the dew point will depend upon the absolute content of water vapor,
that is, the absolute humidity, measured in grams per cubic meter. The dew point of humid air
will be higher than the dew point of dry air. Both air temperature and absolute humidity will
determine what type of condensation will occur when the air is cooled. If air in contact with the
ground is cooled to its dew point, dew or frost will form, dew if the point is above 0°C or frost if
it is below 0°C. Cooling of a larger layer of air near the ground may produce mist or fog, which
freezes if the dew point is below 0°C. Air that is cooled to its dew point by rising and expansion
will condense to form clouds. Above 0°C, small droplets of water are formed. Condensation may
also result in ice crystals at temperatures near or a little below 0°C. When temperatures are near
or a little below 0°C, supercooled water droplets can form.

8
 Let’s Try This

To understand better the process of condensation, do the following activity.

You will need a clear plastic bottle with a cap, a temperature strip (available in pet stores),
some tape and a match.
Tape the temperature strip inside the bottle so that you can read it. Screw the bottle cap on
tightly. Lay the bottle on its side so that you can easily read the temperature strip.
Read and record the temperature of the air inside the bottle. Now, use both hands to
squeeze the bottle as hard as you can. After about one minute, read the strip. Then stop
squeezing and read the temperature strip again after about one minute.
What happened to the temperature when you squeezed the bottle?
_________________________________________________________________________
_________________________________________________________________________
What happened to the temperature after you stopped squeezing the bottle?
_________________________________________________________________________
_________________________________________________________________________
Open the bottle and pour in a few drops of water. Screw the bottle cap on tightly. Swirl the
water around the inside of the bottle so that most of the inside of the bottle is wet. Repeat what
you did earlier.
What happened?
_________________________________________________________________________
_________________________________________________________________________
Lay the bottle on its side, open it and push down to flatten it to about ½ its normal size.
Have someone light a match, blow it out and put it into the bottle while it is still smoldering.
Quickly release the sides of the bottle and put the cap on tightly.
Squeeze the bottle as before very tightly for about one minute. Quickly let the bottle pop
back to its original shape.
What happened?
_________________________________________________________________________
_________________________________________________________________________
In this experiment you saw water molecules condense into a cloud in the bottle. When you
squeezed the bottle the air pressure in it increased which raised the temperature. The warmer air
caused the water in the bottle to evaporate (it became water vapor) and you could not see it.
When you let the bottle pop out, the air pressure in it decreased along with the temperature. This
caused the water molecules to condense into a cloud.

9
 Let’s Learn

Let us look at the next important process in the water cycle below.
Precipitation
All the forms of water that fall from the air to the earth’s surface are called precipitation.
Whether the precipitation is snow, rain, sleet or hail depends on the temperature of the air that the
water falls through. If the temperature is above freezing, the precipitation will most likely be rain.
If the temperature is below freezing, the precipitation will most likely be snow. When air
temperature is only a few degrees above freezing, precipitation may fall as sleet.

Hail is most commonly formed within the cumulonimbus clouds of thunderstorms. Large
updrafts of air can throw rain droplets high up into the tops of the clouds. Here, the temperature
is well below freezing and the droplets freeze. The droplets then fall and can become caught in
further updrafts, adding a second coating of ice to make the hailstones larger. This cycle continues
until the hailstones are too heavy to be lifted again. They then fall as hail. The stronger the updrafts
in the clouds, the longer the hail develops and the larger the hailstones are when they fall.
The amount of rain, sleet, snow or hail which falls in a specified time is expressed as the
depth of water it would produce on a large, level, impermeable surface. Usually it is expressed in
millimeters although inches may sometimes be used. Precipitation is measured daily by means of a
rain gauge. Today’s rain gauges are simple to use with precalibrated scales on their sides. When
measuring precipitation, certain precautions have to be taken against the effects of obstructions,
wind, splashing and evaporation.

Let’s Try This

Make it rain in your kitchen! Do the simple activity below.

You will need a large hand mirror, a freezer or some ice cubes, a potholder or a glove, a
kettle, some water and a stove.
Put the mirror in the freezer or place ice cubes on it to make it really cold. Place water in the
kettle. Then using the stove, bring the water in the kettle to a boil. When the water is boiling, hold
the mirror so that the steam (water vapor) is hitting it. Use a potholder or a glove to protect your
hand. Steam or hot water vapor can burn your skin. Ask someone to hold the mirror for you.

10
 Afterward, write your observations in the space provided below.
___________________________________________________________________________
___________________________________________________________________________
__________________________________________________________________________
_____________________________________________________________________________
Following the steps in the activity will produce rain. The same process that you followed in
doing the activity in your kitchen happens in our environment when it rains. Water vapor goes to
the atmosphere and forms clouds. When the clouds become too heavy, rain falls.

Let’s See What You Have Learned

Match the terms in Column A with their definitions/descriptions in Column B. Write the
letters of the correct answers only in the blanks before the numbers.
Column A Column B
_____ 1. Water a. The instrument used to measure
precipitation
_____ 2. Freezing point
b. Most commonly formed within the
_____ 3. Boiling point
cumulonimbus clouds or thunderstorms
_____ 4. Ice
c. Kind of precipitation that falls when
_____ 5. Glaciers the air temperature is only a few
degrees above freezing point
_____ 6. Ice caps
d. Kind of precipitation that falls when
_____ 7. Avalanches the temperature is above freezing point
_____ 8. Vapor e. Kind of precipitation that falls when
_____ 9. Water cycle the temperature is above freezing point

_____ 10. Aquifer f. All the forms of water that fall from the
air to the earth’s surface
_____ 11. Evaporation
g. The absolute content of water vapor
_____ 12. Transpiration measured in grams per cubic meter
_____ 13. Condensation h. The particular temperature when the
_____ 14. Dew point air becomes saturated

_____ 15. Absolute humidity i. The process whereby water vapor in

the atmosphere is returned to its
_____ 16. Precipitation original liquid state
_____ 17. Rain j. The evaporation of water from plants
_____ 18. Snow k. The process whereby water from the
earth’s surface turn into vapor

11
_____ 19. Sleet l. Bodies of water that act as underground storage
tanks
_____ 20. Hail
m. Involves the short-term, back-and-forth transfer
_____ 21. Rain gauge
of water molecules between the oceans and the
land
n. Water in its gaseous state
o. Large bodies of ice that slowly fall down a slope
or valley under the influence of gravity
p. Layers of ice that form at the north and south
polar regions of the earth
q. Bodies of ice that form in regions where snowfall
exceeds melting
r. What solid water is called
s. 100°C at one atmospheric pressure
t. 0°C at one atmospheric pressure
u. A compound consisting of two atoms of hydrogen
and one atom of oxygen

Compare your answers with those in the Answer Key on page 20. How well did you do?

Let’s Remember

♦ Water is a compound in a liquid state consisting of two atoms of hydrogen and one
atom of oxygen.
♦ Water in its solid form is called ice and in its gaseous state is called vapor.
♦ The water cycle involves the short-term, back-and-forth transfer of water molecules
between the oceans and the land.

12
 LESSON 2

What Is Water For?

Comprising the larger part of the earth’s surface, water is surely the most precious natural
resource that exists on our planet. Without it, life on earth would be nonexistent: it is essential for
everything on our planet to grow and prosper. Although we recognize this fact, we disregard it by
polluting the different bodies of water around us. As a result, we are slowly but surely harming
our planet to the point where organisms are dying at a very alarming rate. In addition to this, our
drinking water as well as the water we use for recreational purposes has been affected. In order
to fight this, we must understand the problems and become part of the solution.
For the purposes of this module, we will only focus on two major problems we are facing at
present—water pollution and salt intrusion.
After studying this lesson, you should be able to:
♦ enumerate the uses of water;
♦ identify the effects of salt intrusion and pollution on the different bodies of water; and
♦ identify possible solutions to these problems.

Let’s Try This

Cross out the pictures that show improper practices that result in water pollution.
_____ 1.

_____ 2.

13
 _____ 3.

_____ 4.

The first and third pictures show practices that can harm the bodies of water around us. The
first can pollute the water by spreading bacteria in the river causing the fish and other living
organisms in the river to get sick and even die. The smoke from the vehicles in the third picture
can pollute the air thereby producing acid rain which can, in turn, pollute the body of water below
the bridge.

Let’s Learn

Water has many important uses. Worldwide, agriculture is the single biggest drain on water
supplies accounting for about 69% of all use. About 23% of water withdrawals go to meet the
demands of industry and energy and just 8% to domestic or household use.
Although much of the world’s farming still relies on the renewable water that falls on crops
from the sky, irrigation largely explains agriculture’s thirst. And the watering of crops has grown
along with rising world population.

14
 Domestic water use—including drinking, food preparation, washing, cleaning, garden and
service industries such as restaurants and laundromats—accounts for only a small portion of total
use in most countries. The amount of water people apply to household purposes tends to increase
with rising standards of living.

Water is also useful as a source of geothermal energy. Geothermal energy comes from the
heat of the earth’s interior used to run the turbines of power plants. These power plants, in turn,
supply electricity to industries and households all over the world.

Water

Electric generator

Turbine blade

Industry, a category that includes energy production, uses water for cooling, processing,
cleaning and removing industrial wastes. Nuclear and fossil-fueled power plants are the single
largest industrial users, applying staggering amounts of water to the job of cooling. While most of
the water used for industrial purposes is returned to the water cycle, it is often contaminated by
chemicals and heavy metals or its temperature is increased affecting the water ecosystems
negatively.

15
 Let’s Review

List down some of the uses of water in the spaces provided below.
1. _________________________________________________________________
2. _________________________________________________________________
3. _________________________________________________________________
Compare what you wrote with the sample answers in the Answer Key on page 20. How
well did you do?

Let’s Learn

Many causes of pollution including sewage and fertilizers contain nutrients such as nitrates
and phosphates. But in excessive levels, these can harm the various organisms in the different
bodies of water. They can clog our waterways and use up dissolved oxygen depriving the other
organisms in the aquatic ecosystems.

Pollution is also caused when silt and other suspended solids such as soil and wastes from
industries and households alike go into bodies of water when it rains. This causes poor respiration
in fishes and other aquatic organisms.
As mentioned earlier, air pollution can cause acid rains thereby affecting the different bodies
of water when they fall as rain. Other factors such as oil spills, wastes from factories and the like
can also cause water pollution.
Polluted water can be harmful not only to the organisms in the various aquatic ecosystems
but also to the people who consume them. In the end, polluted water cannot be used anymore
and so it lessens the amount of useful water.
Another factor that reduces the amount of useful water is salt intrusion. As said earlier, most
of the earth’s water can be found underground. When this water is mixed with salt water, it can
no longer be useful as drinking water. This is because treating salt water is very expensive or most
countries do not have the facilities to do this at all.

16
 Now that you know how the amount of useful water is diminished, what can you do about
it?
The government has been doing its share in passing laws which aim to lessen water
pollution. But is this enough? Clearly, it is not. We all have to do our share in keeping our water
clean and safe for all organisms and for life on earth to continue to exist.

Let’s See What You Have Learned

Think of ways on how you can do your share in maintaining our water safe and clean for all
living things. Make a poster about this. Ask your family members or close friends for some
feedback on how you can make your poster a more effective campaign material. After making
the improvements, post it in a place where a lot of people can see it and keep in mind how
important water is.

Let’s Remember

♦ Water has many different uses—in agriculture: for growing crops; for domestic
purposes: drinking, washing, etc.; as a source of geothermal energy to run power
plants; and in various industries.
♦ Two of the most difficult problems we are facing at present regarding our water supply
are water pollution and salt intrusion.
♦ We all need to do our share in taking care of our water resources for a better future.
Well, this is the end of the module! Congratulations for finishing it. Did you like it? Did you
learn anything useful from it? A summary of its main points is given on the next page to help you
remember them better.

17
 Let’s Sum Up

♦ Water is a compound in a liquid state consisting of two atoms of hydrogen and one
atom of oxygen.
♦ Water in its solid form is called ice and in its gaseous state is called vapor.
♦ The water cycle involves the short-term, back-and-forth transfer of water molecules
between the oceans and the land.
♦ Water has many different uses—in agriculture: for growing crops; for domestic
purposes: drinking, washing, etc.; as a source of geothermal energy to run power
plants; and in various industries.
♦ Two of the most difficult problems we are facing at present regarding our water supply
are water pollution and salt intrusion.
♦ We all need to do our share in taking care of our water resources for a better future.

18
 Answer Key

A. Let’s See What You Already Know (page 2)

1. True
2. False
3. True
4. True
5. True
6. False
7. True
8. True
9. True
10. False

B. Lesson 1
Let’s Study and Analyze (pages 3–4)
1. Bodies of water
2. When there are clouds in the sky
3. By transpiration and evaporation
4. From solid to liquid and then from liquid to gas
Let’s Review (page 5)
Water evaporates from the different bodies of water on the earth’s surface. Water
also transpires from plant leaves to form clouds. When the clouds become too heavy,
the water then falls to the earth’s surface in the form of rain, sleet, hail or snow. The
water then goes back to where it originally came from and the cycle begins anew.

19
 Let’s See What You Have Learned (pages 11–12)
1. (u) 12. (j)
2. (t) 13. (i)
3. (s) 14. (h)
4. (r) 15. (g)
5. (q) 16. (f)
6. (p) 17. (e)
7. (o) 18. (d)
8. (n) 19. (c)
9. (m) 20. (b)
10. (l) 21. (a)
11. (k)

C. Lesson 2
Let’s Review (page 16)
Choose any three from the following:
1. watering crops
2. drinking
3. preparing food
4. washing
5. cleaning
6. watering plants in the garden/backyard
7. source of geothermal energy
8. cooling industrial wastes
9. processing industrial wastes
10. removing industrial wastes

20
 Glossary

Absolute humidity The absolute content of water vapor measured in grams per cubic
meter.
Aquifer A body of water that acts as an underground storage tank.
Avalanche A large body of ice that slowly falls down a slope or valley under the influence
of gravity.
Condensation The process whereby water vapor in the atmosphere is returned to its
original liquid state.
Dew point A particular temperature in which the air becomes saturated.
Evaporation The process wherein water turns into vapor.
Geothermal energy Energy that comes from the heat of the earth’s interior.
Glacier A body of ice that forms in regions where snowfall exceeds melting.
Hail The kind of precipitation most commonly formed within the cumulonimbus clouds of
thunderstorms.
Ice Solid water.
Ice cap A layer of ice that forms at the north and south polar regions of the earth.
Precipitation All the forms of water that fall from the air to the earth’s surface.
Rain The kind of precipitation that falls if the temperature is above freezing point.
Rain gauge The instrument used to measure the amount of precipitation.
Sleet The kind of precipitation that falls if the temperature is only a few degrees above
freezing point.
Snow The kind of precipitation that falls if the temperature is below freezing point.
Transpiration The process of evaporation of water from plant leaves.
Vapor Water in its gaseous state.
Water A compound consisting of two atoms of hydrogen and one atom of oxygen.
Water cycle Involves the short-term, back-and-forth transfer of water molecules between
the oceans and the land.

21
 References

Condensation. http://www.doc.mmu.ac.uk/aric/eae/Weather/Older/Condensation.html.
April 10, 2001, date accessed.
Condensation. http://www-k12.atmos.washington.edu/k12/pilot/water_cycle/
condensation.html. April 10, 2001, date accessed.
East Dakota Water Development District. Pollution Puzzlers. http://www.brookings.com/
bswf/tp16.html. April 10, 2001, date accessed.
Evaporation. http://www.doc.mmu.ac.uk/aric/eae/Weather/Older/Evaporation.html. April
10, 2001, date accessed.
Evaporation. http://www-k12.atmos.washington.edu/k12/pilot/water_cycle/
evaporation.html. April 10, 2001, date accessed.
Krantz, David and Brad Kifferstein. Water Pollution and Society. http://www.umich.edu/-
gs265/society/waterpollution.html. April 10, 2001, date accessed.
Kuecher, Gerald. (1997). New Transport Mechanism Found for Salt Water Intrusion.
http://www.es.anl.gov//htmla/transport/html. April 10, 2001, date accessed.
Precipitation. http://www.doc.mmu.ac.uk/aric/eae/Weather/Older/Precipitation.html. April
10, 2001, date accessed.
Santos, Gil Nonato C. and Jorge P. Ocampo. General Science for High School. Manila,
Philippines: Rex Book Store, 1999.
Science Court, Inc. (1997). Water Cycle. http://www.teachtsp.com/classroom/scicourt/
watercycle.html. April 10, 2001, date accessed.
Transpiration. (1999). http://www.ultranet.com/-jkimbal/BiologyPages/T/
Transpiration.html. April 10, 2001, date accessed.
Water Cycle. http://www.doc.mmu.ac.uk/aric/eae/Weather/Older/Water_Cycle.html. April
10, 2001, date accessed.

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